Multichannel piezoelectric transducer



April 30, @968 ,QM M, W|GG|NS ET Al. 3,381,149

MULTICHANNEL PIEZOELECTRIC TRANSDUCER Filed March 13, 1958 A' IN V43 (20 (fg/5f April 30, w68 A. M. wlGGlNs ET AL 3,381,149

MULTICHANNEL PIEZOELECTRIC TRANSDUCER Filed March 13, 1958 l 3 Sheets-Sheet 3 Graf; jweffzzafzanzzezser Hiller/lays United States Patent O 3,381,149 MULTHCHANNEL PIEZGELECTRIC rIRAFISIIUCEEK Alpha M. Wiggins and .lohn F. Wood, Buchanan, Mich.,

assignors to Electro-Voice, Incorporated, Buchanan,

Mich., a corporation of Delaware Filed Mar. 13, 1958, Ser. No. 721,188 1 Claim. (Ci. S10-8.6)

The present invention relates to electromechanical transducers and to phonograph pickups for simultaneously responding to more than one signal channel.

Recently, phonograph records have been developed with two signal channels recorded in a single groove of the record in order to provide stereophonic reproduction. When recording the record, two separate sound channels are employed, the microphones of the two channels being spaced from each other. The two sound channels are impressed upon the cutting mechanism for the record groove so that a single groove simultaneously carries the modulations of the two recording channels. Two systems are presently being employed to impress the two recording channels upon a single groove. The one system simultaneously modulates the cutting head with the two channels by impressing the channels on the cutting head along axes separated by 90 degrees. Under this system, the modulations of one channel appear as vertical displacements of the record groove, and the modulations of the other channel appear as horizontal displacements. The other system modulates the cutting head along two orthogonally related axes which are each disposed at approximately 45 degrees to the plane of the record. Stereophonic recording has created a need for electromechanical transducers which respond simultaneously to more than one recorded channel.

Electromechanical transducers for responding to more than one channel are not broadly novel. United States Patent No. 1,855,151 to Jones, issued Apr. 19, 1932, and United States Patent No. 2,476,848 to Eckhardt, disclose phonograph pickups for responding to lateral or vertical displacements of a record groove. Also, United States Patent No. 2,114,471 to Keller and Rafuse discloses coil type phonograph pickups for simultaneously reproducing two channels from a single groove of a stereophonic phonograph record which has been recorded at orthogonally related axes disposed at approximately 45 degrees to the surface of the record.

There have been certain drawbacks to the electromechanical transducers known to the art, which are capable of simultaneously reproducing two signal channels from a single record groove. Such transducers tend to have severely limited electrical performance, poor isolation between channels, and high cost.

It is an object of the present invention to provide an electromechanical transducer for simultaneously producing a plurality of electrical responses from mechanical excitation which employs a piezoelectric element, and particularly a piezoelectric element of a polarized articial piezoelectric material.

It is a further object of the present invention to provide a piezoelectric element particularly suitable for phonograph pickups for stereophonic records.

These and additional objects of the present invention will be more fully understood and appreciated from -a further reading of this disclosure, particularly when viewed in the light of the drawings, in which:

FIGURE 1 is a longitudinal sectional view of a phonograph pickup constructed according to the teachings of the present invention;

FIGURE 2 is a sectional View taken along the line 2-2 of FIGURE 1;

ICS

FIGURE 3 is a sectional view taken along the line 3-3 of FIGURE 1;

FIGURE 4 is an end elevational view of the piezo-I electric element of FIGURES l through 3 illustrating the polarization axes thereof;

FIGURE 5 is a transverse sectional view of a piezoelectric element constituting another embodiment of the present invention;

FIGURE 6 is a transverse sectional view of another piezoelectric element which is another embodiment of this invention;

FIGURE 7 is an end elevational view of a piezoelec- Itric element constituting a further embodiment of this invention;

FIGURE 8 is also an end elevational view of a piezoelectric element which forms another embodiment of the present invention;

FIGURE 9 is an end elevational view of a piezoelectric element which is still another embodiment of the present invention;

FIGURE 10 is a schematic electrical circuit diagram showing a stereophonic pickup connected to respond only to lateral record undulations;

FIGURE 11 is a schematic electrical circuit diagram showing a stereophonic pickup connected to respond only to vertical record undulations;

FIGURE l2 is an electrical circuit diagram schematically illustrating a series connected stereophonic pickup connected between the inputs of two sound systems;

FIGURE 13 is a schematic electrical circuit diagram illustrating a parallel connected stereophonic pickup connected between the inputs of two sound systems; and

FIGURE 14 is a schematic electrical circuit diagram showing a stereophonic pickup connected between the inputs of two push pull amplifiers of two sound systems.

The inventors have found that a piezoelectric element may be used to produce a plurality of electrical responses to an applied mechanical force which are related to cornponents of the applied force. A piezoelectric element with a plurality of pairs of spaced electrodes, each pair having electrodes on opposite sides of the axis of the element, produces an electrical response on each pair of electrodes to an impressed force related in magnitude to the component of the force exerted through the angle between the direction of the applied force and the axis between the electrodes of the pair. A piezoelectric element constructed according to the teachings of the present invention has a plurality of elongated sections of piezoelectric material in which each section confronts another section located on the opposite side of the axis of elongation of the piezoelectric element. The piezoelectric sections are mechanically interconnected or parts of a single unitary structure, so that bending of the element results in elongation of one of the sections and compression of the,

other section disposed in the plane of the bend. The sections are provided with electrodes on their exterior surface, so that bending of the element results in the generation of potentials on the electrodes which may be connected in an electrical circuit in an additive manner. By orienting the axes between two pairs of electrodes of a piezoelectric element with the recording axes of a stereophonic record, elect-rical signals are produced on the two pairs of electrodes responsive to the two recorded channels on the record groove.

Although it is to be understood that a piezoelectric element constructed according to the present invention has many utilities as an electromechanical transducer, such an element has particular advantages when employed as a phonograph pickup, and for that reason is so illustrated in FIGURES 1 through 3. As illustrated, the pickup has a cartridge casing it) which is removably positioned within a sleeve 12 of a mounting mechanism for securing the pickup to the tone arm of a phonograph. The details of the means for mounting the pickup to the tone arm are disclosed in the U.S. patent of Wood No. 2,793,254, entitled Cartridge Case and Turnover Mechanism, issued May 21, 1957. The casing is generally a hollow cylinder, has a closed end 14, and is open at the opposite end 16.

A number of piezoelectric elements, generally referred to as 19, are disclosed herein, and one of these elements 19A is illustrated `as the transducer of the pickup of FIG- URES 1 through 3. The element 19A has an elongated body 18 of artificial piezoelectric material disposed along the axis of the casing 10. The term artificial piezoelectric material is employed herein to dene a dielectric material which is conditioned by the application of a unidirectional electric potential to provide a substantial transducing-response characteristic as between mechanical signal energy and electrostatic field signal energy. The body 18 is mounted to the closed end 14 of the casing 19 by mounting means pivotal in all directions attached to the inner end of the element, as illustrated in FIGURE 2 and described hereinafter, and a snubber ring Ztl is disposed about the body 18 approximately at its center. The ring 20 is constructed of resilient material, such as rubber.

The body 18 is an elongated quadrangular rod of polarized polycrystalline dielectric material, such as barium titanate (BaTiOa), or strontium titanate with a ceramic binder. Lead zirconium titanate is also a very satisfactory material. The four flat surfaces parallel to the axis of elongation of the body 1S are provided with two pairs of electrodes 22 and 24, and 26 and 28, these electrodes being in contact with the -body 18 and electrically insulated from each other. The electrodes are thus in two pairs, a pair 'being two electrodes disposed on opposite sides of the axis of the body 18. The body 18 and electrodes 22, 24, 26, and 28 constitute the piezoelectric element 19A.

Electric contact to each of the four electrodes 22, 24, 26, and 28 and mounting of the element to the casing can be achieved in the pivotal manner illustrated herein, which is a modification of the hinge-like element mounting disclosed in U.S. Patent No. 2,793,254, or by mounting means employing resilient material such as disclosed in the patent application of Wood entitled Electromechanical Transducer, Ser. No. 446,255, now Patent No. 2,851,- 541. It is also possible to mount the element rigidly at one end to the casing with a loss of electrical and mechanical performance. As illustrated in FIGURE 2, the end of the piezoelectric element adjacent to the closed end 14 of the casing 10 is pivotally secured between four metallic contact blades 30, 32, 34, and 36, the contact blades being anchored in openings 38 in the casing 1t). Each of the blades 30, 32, 34, and 36 contacts one of the electrodes 22, 24, 26, or 28 adjacent to one end thereof, and is in slip contact with a contact 40 adjacent to the other end thereof. The contacts 40 extend through the closed end of the sleeve 12 to provide terminals for electrical connections. p

A rigid body or cap 42 is rigidly secured to the end of the piezoelectric body 18 opposite the closed end 14 of the casing 10, and the cap extend-s through the open end 16 of the casing 10 along the axis of the piezoelectric body 18. For best results, the cap must be constructed of noncompliant material, such as plastic, and should have small mass. A short rigid stylus 44 is rigidly mounted near the end of the `cap 42 opposite the piezoelectric body 18, and the stylus 44 is adapted to ride in the groove of a stereophonic microgroove record. To achieve best results, the tip of the stylus 44 is disposed on the axis of the piezoelectric body 18. A second larger stylus 46 is also embedded in the cap 42, and hence rigidly mounted thereto, on the side of the cap opposite `the stylus 44 for tran- 4 scribing records with wider grooves. Since record-s of the latter type generally are not stereophonic recordings, it is not necessary that the tip of this stylus 46 also be on the axis of the piezoelectric body 1S.

The body 18 and the electrodes 22, 24, 26, and 23 form a bender type piezoelectric element, that is an element that produces an electrical response from bending. Electrical response from twisting is substantially avoided by placing the tip of the stylus 44 on the axis of the body 18. Since the electrical response to a given amplitude of mechanical force impressed `along each of the axes between pairs of electrodes preferably is essentially the same, the piezoelectric body 18 is preferablyone of a group of artii'cial piezoelectric materials. Polycrystalline titanate dielectric material is such an articial piezoelectric material. Such materials exhibit piezoelectric properties after being charged by a relatively high potential. The body 18 is charged lby connecting the positive terminal of a potential source to one pair of electrodes, Ia pair being two electrodes on opposite sides of the axis of the body 18, :and the negative terminal of the source to the other pair of electrodes. The resulting vectors of polarization of the body 18 'are illustrated in FIGURE 4.

The stylus 44 is disposed in a plane normal to the surface `of the record, 'and must be oriented relative to the piezoelectric element to 'approximately 'align the `axes between the pairs of electrodes with the axes employed to record the two channels on the stereophonic record. Where the one recording axis is vertical and the other horizontal, the stylus is disposed in the plane of the vertical recording taxis, and the axis between one of the pairs of electrodes is also disposed in this plane. However, Where the two recording axes are orthogonally related at 45 degree angles to `the piane of the record, the stylus is secured to the piezoelectric element in ya plane bisecting the angle between the -axe`s of the pairs of electrodes.

FIGURE 5 illustrates 1a modified form off piezoelectric element suitable for the element 19 in the pickup illustrated in FIGURES 1 through 3. Throughout this `specication, the same reference numerals lare employed for identical elements. The element, designated 19B, is elongated land has a conductor 47 between the electrodes in the =form of an elongated X-shaped conducting member 48, and tour elongated bars 50, 52, 54, and 56 with square Lcross-section abutting the center con-ducting member 48. The bars 50, 52, 54, and 56 are constructed of articial piezoelectric material, Aas described above, and are mounted to the center member 48. The center member 48 may be in the -form of `a coating disposed upon two adjacent surfaces of each bar, or may be formed of thin sheets of electric-ally conducting material secured together to form the X-shaped member. Two pairs of electrodes 22 and 24, and 26 and 28 are mounted to the surfaces of the assembled blocks, the electrode 22 abutting the surfaces of blocks 5G and 52, the electrode 26 y'abutting the surfaces of blocks 52 and 54, the electro-de 24 abutting the surfaces olf blocks 54 Iand 56, `and the electrode 28 abutting the 'surfaces odi block-s Stil and 50. Each of the electrodes is electrically insulated lfrom the other electrodes and also from `the center member 48. The center member 48 is spaced from the electrodes for this reason. The artificial piezoelectric material may be polarized by yconnecting one yterminal of a potential source to the center conductor 48 and the other terminal to each of the electrodes 22, 24, 26, and 28. VAccess to the center member 48 may be had at the ends of the elongated element 19B. If it is assumed that the electrodes .are connected to the positive terminal of the polarizing potential source and the center member 48 to the negative terminal, the direction of polarization will be that `indicated by the |arrows in FIGURE 5.

The element 19B may be employed in the mounting structure of FIGURE 1, and will produce signal voltages on the two pairs of opposite electrodes as a result of deilections described above for the element 19A.

FIGURE 6 illustrates another embodiment of a piezoelectric element 19 suitable for use in the pickup illustrated in the FIGURES 1 through 3 :and designated 19C. In the element 19C, van elongated quadrangular body 66 of artificial piezoelectric material, as described above, is provided with two pairs of electrodes on its side surfaces, designated 22 and 24, and 26 and 28. These electrodes are parallel to the axis of elongation of the body 66. The body I66 is also provided 'with a plurality of parallel channels 76 disposed in two orthogonally related planes Iwhich intersect at the axis of the body 66. The channels 76 are parallel to the axis of the body and equally spaced from each other in each plane. Each of the channel-s 66 is provided ywith Ian electrically conducting coating 78, for examplle of 'aqu-adag, or sprayed graphite.

The tbody `66 is polarized by connecting one terminal of a potential source to each of the electrodes 22, 24, 26, and 28, Iand connecting the other electrode of the potential source to the electrically conducting coating 78 on each of the channels 76. This results in the same polarization axes indicated in FIGURE 5. It is thus clea-r, that the channels 76 and the electrically conducting coatings 78 constitute a center conductor 47 similar to that of the embodiment illustrated in FIGURE 5.

As illustrated in FIGURE 7, the center conductor 47 may 'be formed on the surfaces of a single opening 80 which has :an X-shaped cross-section in `a piezoelectric body, here `designated 66A. The opening 80 has a first relatively thin portion 82 which extends through the axis off the body 66A transversely between the pair of electrodes 22 and 24, 1an-d a second relatively thin portion 84 which extends through the axis of the body 66A transversely between the pair of electrodes 26 and 28. The opening 80 is provided with an electrically conducting coating 86, Iand the body 66A may be polarized .by connecting the potential source between the electrodes 22, 24, 26, and 28 and the electrically conducting coating 86. This piezoelectric element is designated 19D in FIGURE 7 and may Ibe employed in the pickup illustrated in FIGURES l through 3.

FIGURE 8 illustrates 'a further modification of the piezoelectric element, designated 19E. An elongated quadrangular piezoelectric body 66B is provided with two pairs of electrodes 22, 24 and 26, 28. In the element 19E, a cylindrical opening 88 extends through the body 66B about the axis of elongation of the body, and a coating 90 of electrically conducting material is disposed upon the surface of the opening 88. The body 66B is also of artificial piezoelectric material, and polarization may be achieved by connecting the coating 90 of electrically conducting material to one terminal of the power source land the electrodes 22, 24, 26 and 28 to the other terminal of the power source. Assuming the coating 90 to be negative, the axes of polarization are indicated by the arrows in FIGURE 8.

FIGURE 9 illustrates another modification of the piezoelectric element designated 19E. In this element 19F, Aan artificial piezoelectric body 92 in the form of a hollow cylinder is provided with two pairs of confronting electrodes, the one pair 94 and 96 and the other pair 98 and .100. The electrodes are curved on the same radius as the outer surface of the body 92, and electrodes in each pair are disposed on opposite sides of the axis of the body. A coating 102 of electrically conducting material is disposed on the inner surface of the body 92. The artificial piezoelectric body 92 may be polarized by connecting the coating 102 to one terminal of a direct current power source, and the electrodes 94, 96, 98, and 100 to the other terminal of the power source. Assuming the coating 102 to be connected to the negative terminal of the power source, the polarization vectors are as indicated by the arrows in FIGURE 9. One of the advantages of the element 19F is that the distance between the coating 102 and each of the electrodes is essentially constant, so that a given polarizing potential will achieve more uniform polarization of the artificial piezoelectric material. Further, it may be less expensive with some processes to construct a hollow cylindrical body 92 of artificial piezoelectric material than other shapes of bodies.

FIGURES 10 and 11 show the monaural electrical connections for using a stereo pickup. FIGURE 10 shows the connections which will produce a maximum response for lateral undulations only of a record groove, and FIG- URE 11 the connections for maximum response to only vertical undulations of a record groove. The piezoelectric element 19 may be any one of the elements previously described, and lfor simplicity the same reference numerals 22, 24, 26, and 28 are employed for the two pairs of electrodes, although it is to be understood that these FIG- URES 10 through 13 apply equally to element 19F. In FIGURES 10 and 11, the stylus is shown schematically and designated 104, and the stylus is mounted to one side of the piezoelectric element y19 on a plane passing through the axis of the element. In FIGURE l0, the element is connected to respond only to lateral undulations of a record, and in FIGURE 11 the element is connected to respond to vertical undulations of the record groove.

FIGURES 12 and 13 illustrate the element 19 connected in an electronic circuit for reproduction from a stereophonic record. In FIGURES 12 and 13, the stylus 104 is secured to a corner of the element 19, although the circuits are equally applicable to stereophonic records having vertical and lateral channels. The electrodes 22 and 28 are connected to the input terminal 105 of two identical amplifiers 106 and `108 of two sound reproducing systems, respectively. The other electrode 24 of the first pair of electrodes is connected to the input terminal 109 of the amplifier 106, while the other electrode 26 of the second pair is connected to the input terminal 109 of the amplifier 108. For illustrative purposes, the input stages of the amplifiers are shown with a vacuum tube 4110 having .a cathode 112 connected to terminal 105 and a plate 114. Each tube .110 also has a grid 116 which is connected through a capacitor 118 to the input terminal 109 of the amplifier. A grid resistor 122 is also connected between the grid 116 and terminal 10S of each amplifier.

In use, record undulations transmitted by the stylus 104 to the piezoelectric element 19 along an axis between the electrodes 26 and 28 will generate potentials across these electrodes which are impressed upon the amplifier 108. In like manner, the undulations along the axis between the electrodes 22 and 24 produce potentials across these electrodes which are transmitted t0 the amplifier `106. Because of the fact that bending of the element 19 along 'an axis parallel to the axis between either pair of electrodes produces potentials primarily upon that pair of electrodes, the piezoelectric element is effective to pick up the material recorded on two record channels and transmit electrical signals responsive to the channels to separate amplifiers.

FIGURE l2 illustrates the element 19 connected in 'a circuit between the two amplifiers in which two sections of the element are connected in a series at the input of each amplifier. In order to produce electrical output connected in this manner, the element must be polarized in opposite directions adjacent to the electrodes of each pair. This can be accomplished by polarizing from a center conductor to the electrodes, as illustrated in FIG- URES 5 through 9, or between adjacent electrodes as in FIGURE 4.

The element 19 may be connected in a parallel circuit between the two amplifiers, as illustrated in FIGURE 13. if it has a conductor 47 between the electrodes and is diagonally polarized, that is polarized by connecting the positive terminal of a direct current s-ource to two adjacent electrodes and the negative terminal to the other two adjacent electrodes. The electrodes 22, 24, and 26, 28 of each pair are interconnected, and connected to the ungrounded input terminal 109 of the amplifiers 106 and 108, respectively. The conductor 47 is connected to the grounded input terminal 105 of both amplifiers. Superior electrical isolation between channels is obtained with this circuit.

FIGURE 14 illustrates the element 19 connected to the push pull input circuits of two potential responsive means which may be amplifiers 106A and 108A. This circuit will produce isolation between channels equivalent to that of FIGURE 13 Without employing a conductor 47 between the electrodes. Each of the amplifiers has an input terminal 124 connected to the common ground of that ampliier, and the terminals 124 of the two amplifiers are interconnected. The amplifiers 106A and 108A also have input terminals 126 and 128, and these terminals of amplifier 106A are connected to the electrodes 22 and 24 of one pair of electrodes, respectively. In like manner, the electrodes 26 and 28 of the other pair are connected to the input terminals 128 and 126, respectively, of the other amplifier 108A. Each of the amplifiers 106A and 108A has a pair of vacuum tubes 130 and 132 connected in push pull. As illustrated, the tubes 130 and 132 have interconnected current return electrodes 134 which are connected to the grounded input terminal 124, and grids 136 and 138 connected to the input terminals 126 and 128 through capacitors 140 and 142, respectively. The element 19 is polarized as indicated in FIGURE 4.

While the elements described above have particular utilities in photograph pickups, they may also be employed in inertial guidance systems, accelerometers or other applications where multiple coordinate pickup is desired. Also, an element with two pairs of electrodes produces greatest isolation between channels, but for some applications a larger number of pairs of electrodes may be employed. It is, therefore, intended that the scope of the present invention be not limited by the foregoing disc1osure,but only by the appended claim.

The invention claimed is:

1. An electromechanical transducer comprising an elongated body of artificial piezoelectric material having a rectangular cross section, said body having a plurality of channels parallel to the axis of elongation of the body and disposed in two orthogonal planes intersecting the 8 axis of the body, a coating of electrically conducting material disposed on the surface of each of the channels, and two pairs of electrodes disposed on the surface of the body, the electrodes of each pair being disposed on opposite sides of the axis of the body and electrically insulated from each other.

References Cited UNITED STATES PATENTS 1,869,556 8/1932 Giebe et al. 31o-9.6 1,874,960 8/1932 Giebe et al. S10-9.7 1,906,214 4/ 1933 Nicolson 179-100.41 1,907,427 5/1933 Marrison 3 10--8.l 1,930,536 10/1933 Pierson B10-8.2 2,093,540 9/ 1937 Blumlein 179--100.41 2,271,200 1/ 1942 Mason 3l09.7 2,387,472 10/ 1945 Sontheimer 310--8 2,439,499 4/ 1948 Williams et al. 179-100.41 2,476,848 7/ 1949 Eckhardt et al. 179-100.41 2,515,446 7/1950 Gravley 179-100.41 2,518,348 8/1950 Mason 310-9.6 2,540,412 2/1951 Adler 179--10041 2,596,494 5/ 1952 Lynch 179--100.41 2,775,460 12/ 1956 Shivack 179-100.41 2,834,158 5/1958 Peterman 179-100.41 2,900,536 8/1959 Palo 179-100.41 2,944,117 7/1960 Gray 179-100.41 2,851,541 9/1958 Wood 179--100.41 2,838,696 6/1958 Thurston S10-8.5 2,625,663 l/ 1953 Howatt 179-100.41 3,073,914 1/1963 Germano 179-10041 2,838,695 6/1958 Thurston B10- 8.5 1,907,425 5 1933 Marrison 31o-9.6

BERNARD KONICK, Primary Examiner.

IRVING S. SRAGOW, NEWTON LOVEWELL, L. M. ANDRUS, JAMES W. MOFI'IT, V. S. YAFFE, Examiners.

M. S. GITTES, M. K. KIRK, H. S. WILLIAMS, W. L. LYNDE, I. R. HOPKINS, M. REICH, Assistant Examiners. 

1. AN ELECTROMECHANICAL TRANSUDCER COMPRISING AN ELONGATED BODY OF ARTIFICIAL PIEZOELECTRIC MATERIAL HAVING A RECTANGULAR CROSS SECTION, SAID BODY HAVING A PLURALITY OF CHANNELS PARALLEL TO THE AXIS OF ELONGATION OF THE BODY AND DISPOSED IN TWO ORTHOGONAL PLANES INTERSECTING THE AXIS OF THE BODY, A COATING OF ELECTRICALLY CONDUCTING MATERIAL DISPOSED ON THE SURFACE OF EACH OF THE CHANNELS, AND TWO PAIRS OF ELECTRODES DISPOSED ON THE SURFACE OF THE BODY, THE ELECTRODES OF EACH PAIR BEING DISPOSED ON OPPOSITE SIDES OF THE AXIS OF THE BODY AND ELECTRICALLY INSULATED FROM EACH OTHER. 